It is well known to utilize ultrasonic sealing techniques for forming seals in polymeric materials. United States patents disclosing the use of ultrasonic techniques are U.S. Pat. Nos. 3,468,731 to Obeda, 4,075,046 to McDonald, 4,190,690 to Rabeneck et al, and 4,333,791 to Onishi.
The Obeda patent discloses an ultrasonic sealing apparatus for sealing the end portion of thermoplastic tubular containers. The end portion of a tubular container is placed in contact with an anvil, and an ultrasonic sealing horn is brought into pressing engagement with the end portion to produce the desired ultrasonic seal.
The McDonald patent relates to the formation of rigid portions in flexible structures utilizing an ultrasonic sealing device, and is particularly directed to the fabrication of shoelaces having rigid tips. In operation, a shoelace material is placed in a parallel-walled slot in an anvil, and an ultrasonic sealing horn is moved downwardly into pressing engagement with the material to effect formation of the rigidified portion.
The Rabeneck et al patent discloses a method and apparatus for the manufacture of sealed-end tubular thermoplastic net bagging. In operation, an ultrasonic sealer is mounted for vertical reciprocal movement into pressing engagement with netting feedstock which has been twisted, followed by sealing to form an integral seal nugget.
The Onishi patent relates to an ultrasonic seam welding apparatus for seam welding together sheet-like workpieces piled on top of each other. The workpieces are positioned above a vertically movable ultrasonic sealing horn, and pressure is imparted to the workpieces by raising the ultrasonic sealing horn to urge the workpieces into contact with a roller assembly located above the workpieces.
It has now been found that a need exists for a device which can be used for ultrasonically sealing bagging material containing products to form sealed product-containing bags having ultrasonic seals at one or both ends. This application finds particular utility in the produce industry, especially in the packaging of meat and poultry, where such a device would facilitate the formation of produce-containing bags having ultrasonic seals at one or both ends which ultimately could be used in a microwave oven for cooking or defrosting, due to the absence of metal clips or other metal components in the bag. Such a device would have to be easy to use by produce packers and be capable of adjustment for sealing different types of bagging material. The device would also have to be waterproof so as to permit a wash-down at the end of a day's usage, in accordance with usual hygiene standards associated with the food processing and packaging industries. Such a device has now been developed by the present inventors and this is described below.